1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used as a transmission for a vehicle or various kinds of industrial machines.
2. Description of the Related Art
As a transmission for a vehicle, use of such a toroidal-type continuously variable transmission as schematically shown in FIGS. 4 and 5 has been executed in part of the vehicle industry. In this toroidal-type continuously variable transmission, for example, as disclosed in JP-UM-A-62-71465, an input side disk 2 serving as a first disk is supported concentrically with an input shaft 1, and an output side disk 4 serving as a second disk is fixed to the end portion of an output shaft 3 which is disposed concentrically with the input shaft 1. In the interior of a casing in which the toroidal-type continuously variable transmission is stored, there are disposed trunnions 6, 6 which can be respectively swung about their associated pivot shafts 5, 5 disposed at positions twisted with respect to the input shaft 1 and output shaft 3. On the respective trunnions 6, 6, there are rotatably supported power rollers 11, while the power rollers 11, 11 are respectively held by and between the input side and output side disks 2, 4.
Each of the sections of the mutually opposed inner surfaces 2a, 4a of the input side and output side disks 2, 4 provides a concave surface which can be obtained by rotating an arc with the pivot shaft 5 as a center thereof or a curved line resembling this arc. And, the peripheral surfaces 11a, 11a, which are respectively formed as spherically convex surfaces, of the power rollers 11, 11 are contacted with the inner surfaces 2a, 4a. 
Between the input shaft 1 and input side disk 2, there is interposed a pressing device 12 of a loading cam type. The pressing device 12 presses the input side disk 2 toward the output side disk 4 elastically. Also, the pressing device 12 includes a cam plate 13 rotatable together with the input shaft 1 and a plurality of (for example, four) rollers 15, 15 held in a retainer 14. Also, on one side surface (in FIGS. 4 and 5, the left side surface) of the cam plate 13, there is formed a cam surface 16 being a curved surface extending in the peripheral direction of the cam plate 13; and, on the outer surface (in FIGS. 4 and 5, the right side surface) of the input side disk 2 as well, there is formed a similar cam surface 17. And, the plurality of rollers 15, 15 are supported in such a manner that they can be rotated about their respective shafts extending in the radial direction with respect to the input shaft 1.
In the thus-structured toroidal-type continuously variable transmission, in case where the input shaft 1 is rotated, the cam plate 13 is rotated with the rotation of the input shaft 1 and the cam surface 16 presses the plurality of rollers 15, 15 against the cam surface 17 formed on the outer surface of the input side disk 2. As a result of this, at the same time when the input side disk 2 is pressed against the plurality of power rollers 11, 11, the input side disk 2 is rotated due to the mutual pressing actions between the pair of cam surfaces 16, 17 and the rolling surfaces of the plurality of rollers 15, 15. And, the rotation of the input side disk 2 is transmitted through the power rollers 11, 11 to the output side disk 4, so that the output shaft 3 fixed to the output side disk 4 is rotated.
Now, description will be given below of a case where the rotation speed between the input shaft 1 and output shaft 3 is to be changed. Firstly, to reduce the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 are swung about the pivot shafts 5, 5 to incline displacement shafts 9, 9 so that the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 4, can be respectively contacted with the near-to-center portion of the inner surface 2a of the input side disk 2 and the near-to-outer-periphery portion of the inner surface 4a of the output side disk 4.
On the other hand, to increase the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 are swung about the pivot shafts 5, 5 to incline the displacement shafts 9, 9 so that the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 5, can be respectively contacted with the near-to-outer-periphery portion of the inner surface 2a of the input side disk 2 and the near-to-center portion of the inner surface 4a of the output side disk 4. And, in case where the inclination angles of the displacement shafts 9, 9 are set intermediate between FIGS. 4 and 5, there can be obtained an intermediate speed ratio between the input shaft 1 and output shaft 3.
Further, FIGS. 6 and 7 show a conventionally known toroidal-type continuously variable transmission. In this conventional toroidal-type continuously variable transmission, an input side disk 2 and an output side disk 4 are respectively supported on the periphery of a circular-pipe-shaped input shaft 18 through needle roller bearings 19, 19 in such a manner that they can be rotated and can be shifted in the axial direction thereof. Also, a cam plate 13 constituting a pressing device 12 of a loading cam type is spline engaged with the outer peripheral surface of the end portion (in FIG. 6, the left end portion) of the input shaft 18 and is prevented from moving in a direction to part away from the input side disk 2 by a flange portion 20. Also, an output gear 21 is connected to the output side disk 4 by keys 22, 22, so that the output side disk 4 and output gear 21 can be rotated in synchronization with each other.
Similarly to the structure shown in FIGS. 4 and 5, in the interior of a casing in which the toroidal-type continuously variable transmission is stored, there are disposed a pair of trunnions 6, 6 which can be respectively swung about their associated pivot shafts (inclined shafts) 5, 5 disposed at positions twisted with respect to the input shaft 18. Each of the trunnions 6, 6, as shown in FIG. 7 (in FIG. 7, only one trunnion is shown. Therefore, in FIG. 7, composing elements accompanying the trunnion (not shown) are not shown either.) includes a pair of bent wall portions 8, 8 which are formed on the both ends in the longitudinal-direction (in FIG. 7, the right and left direction) of a support plate portion 7 in such a manner that they are bent on the inner surface side (in FIG. 7, the lower side) of the support plate portion 7. And, due to the bent wall portions 8, 8, in the trunnion 6, there is formed a recess-shaped pocket portion P for storing a power roller 11 therein. Also, on the outer surfaces (the opposite surfaces to the support plate portion 7) of the respective bent wall portions 8, 8, there are disposed pivot shafts 5, 5 in such a manner that they are concentric with each other.
In the central portion of the support plate portion 7, there is formed a circular hole 10, while the base end portion 9a of a displacement shaft 9 is supported in the circular hole 10. And, in case where the trunnions 6, 6 are swung about the pivot shafts 5, 5, the inclination angles of the displacement shafts 9 respectively supported on the central portions of the trunnions 6, 6 can be adjusted. Also, on the peripheries of the leading end portions 9b of the displacement shafts 9 which project from the inner surfaces of the trunnions 6, 6, there are rotatably supported the power rollers 11; and, the power rollers 11, 11 are respectively held by and between the input side and output side disks 2, 4. By the way, the base end portions 9a and leading end portions 9b of the displacement shafts 9, 9 are eccentric to each other.
As shown in FIG. 7, the two end portions of each of the pair of trunnions 6, 6 are supported in such a manner that they can be swung and shifted in the axial direction (in FIG. 6, the front and back direction; and, in FIG. 7, the right and left direction) with respect to a pair of support plates 23, 23. And, as described before, in the circular hole 10 formed in the central portion of each of the support plate portions 7 constituting the trunnions 6, 6, there is rotatably supported the base end portion 9a of the displacement shaft 9 structured such that the base end portions 9a and leading end portions 9b thereof are parallel to and eccentric to each other. Also, on the leading end portion 9b of each of the displacement shafts 9 projecting from the inner surface of each of the support plate portions 7, there is rotatably supported the power roller 11.
By the way, a pair of displacement shafts 9, 9 provided in each of the pair of trunnions 6, 6 are disposed on the mutually 180° opposite positions with respect to the input shaft 18. Also, while the leading end portion 9b of each of the displacement shafts 9, 9 is eccentric to the base end portion 9a thereof, the eccentric direction of the leading end portion 9b to the base end portion 9a is the same direction (in FIG. 7, the reversed right and left direction) with respect to the rotation direction of the input side and output side disks 2, 4. Also, the eccentric direction is a direction substantially perpendicular to the arrangement direction of the input shaft 18. Therefore, the power rollers 11, 11 are supported in such a manner that they can be slightly shifted in the longitudinal direction of the input shaft 18. As a result of this, even when the power rollers 11, 11 tend to shift in the axial direction of the input shaft 18 due to the elastic deformation of the respective composing parts caused by thrust loads generated by the pressing device 12, the shifting movements of the power rollers can be absorbed without applying unreasonable forces to the composing parts.
Also, between the outer surfaces of the power rollers 11, 11 and the inner surface of the support plate portion 7 constituting the trunnions 6, 6, there are interposed a thrust ball bearing 24, which is a thrust rolling bearing, and a thrust needle roller bearing 25 in the order starting from the outer surface of the power roller 11. Each thrust ball bearing 24, while supporting a thrust-direction load applied to its associated power roller 11, allows the power roller 11 to rotate. Each thrust ball bearing 24 includes a plurality of balls 26, 26, a circular-ring-shaped retainer 27 for holding the balls 26, 26 in a rollable manner, and a circular-ring-shaped outer race 28. Also, the inner race raceway of each thrust ball bearing 24 is formed in the outer surface of its associated power roller 11, whereas the outer race raceway thereof is formed in the inner surface of its associated outer race 28.
Also, each of the thrust needle roller bearings 25 is held by and between the inner surface of the support plate portion 7 constituting its associated trunnion 6 and the outer surface of its associated outer race 28. Each thrust needle roller bearing 25, while supporting a thrust load applied to its associated outer race 28 from its associated power roller 11, allows the power roller 11 and outer race 28 to be swung and shifted about the base end portion 9a of its associated displacement shaft 9.
Further, on one end portion (in Fig. the right end portion) of each of the trunnions 6, 6, there is disposed a drive rod 29; and, on the outer peripheral surface of the middle portion of each drive rod 29, there is fixedly disposed a drive piston 30 (an oil pressure piston). And, these drive pistons 30 are respectively fitted and mounted into their associated drive cylinders 31 in an oil-tight manner.
In the case of the thus-structured toroidal-type continuously variable transmission, the rotation power of the input shaft 18 is transmitted through the pressing device 12 to the input side disk 2. And, the rotation power of the input side disk 2 is transmitted through the pair of power rollers 11, 11 to the output side disk 4 and further the rotation power of the output side disk 4 is taken out by the output gear 21.
To change the rotation ratio between the input shaft 18 and output gear 21, the pair of drive pistons 30, 30 may be shifted in the mutually opposite directions. The pair of trunnions 6, 6 are shifted in the mutually opposite directions in accordance with the shifting of the two drive pistons 30, 30. For example, the power roller 11 (not shown) situated on the lower side in FIG. 7 is shifted to the right, while the power roller 11 of FIG. 7 situated on the upper side is shifted to the left. This changes the direction of a tangential-direction force acting on the contact portions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a of the input side and output side disks 2 and 4. And, as the direction of this force is changed, the trunnions 6, 6 are respectively swung in the mutually opposite directions about their associated pivot shafts 5, 5 that are pivotally supported on the support plates 23, 23.
As a result of this, as shown in the above-mentioned FIGS. 4 and 5, the contact positions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a of the input side and output side disks 2 and 4 are changed, so that the rotation ratio between the input shaft 18 and output gear 21 is changed. Also, in a case where a torque to be transmitted between the input shaft 18 and output gear 21 is varied and the elastic deformation amounts of the composing parts are thereby varied, the power rollers 11, 11 and outer races 28 associated with these power rollers 11 are slightly rotated about the base end portions 9a of their associated displacement shafts 9, respectively. Between the outer surfaces of the outer races 28 and the inner surfaces of the support plate portions 7 constituting the trunnions 6, there are interposed the thrust needle roller bearings 25 and, therefore, the above rotational movements of the power rollers and outer races are executed smoothly. Accordingly, as described before, there is required only a small force to change the inclination angles of the displacement shafts 9, 9.
As described before, in the toroidal-type continuously variable transmission, by applying a pressure difference to an oil pressure piston 30 fixedly disposed on a drive rod (which is hereinafter referred to as a trunnion shaft) 29 extending from one end of the pivot shaft 5 of the trunnion 6, the trunnion 6 can be moved along the inclined rotation axis direction thereof. In this case, the oil pressure piston 30 is disposed on each of the trunnions 6; however, generally, the oil pressure is controlled using the inclined rotation angle of only one trunnion 6 (the angle of swing about the pivot shaft 5 thereof) (see e.g. JP-2-163567).
Also, the oil pressure piston 30, as described before, is fitted with the outer surface of the trunnion shaft 29 in such a manner that the trunnion shaft 29 penetrate through the oil pressure piston 30. Therefore, in the case of the trunnion 6 and trunnion shaft 29, they are formed separately from each other and, after then, they are connected together by a pin.
However, in case where the case of the trunnion 6 and trunnion shaft 29 are formed separately and are then connected together by a pin in this manner, not only the number of manufacturing steps thereof increases (to thereby the manufacturing cost thereof increases) but also the assembling precision of the trunnion 6 and trunnion shaft 29 is lowered. In view of this, there is proposed a technique in which the trunnion 6 and trunnion shaft 29 are formed as an integral body.
By the way, in case where the trunnion 6 and trunnion shaft 29 are formed as an integral body, there arises a problem as to how to form lubricating oil passages to the thrust needle roller bearing 24 and thrust ball bearing 25. Especially, since the thrust ball bearing (bearing) 24 supporting the power roller 11 is rotating at a high speed under a large load, it generates large calorific value. Therefore, a sufficient quantity of lubricating oil must be supplied to the thrust ball bearing 24.
As a general method for forming the lubricating oil passages when the trunnion 6 and trunnion shaft 29 are formed as an integral body, as shown in FIG. 7, the end portion of the trunnion shaft 29 is worked using a drill to form, in the interior of the trunnion shaft 29, a long oil hole 40 having a small diameter and extending in the axial direction of the trunnion shaft 29, and further a plug 44 is press-fitted into the thus worked end portion of the trunnion shaft 29 to thereby secure an oil passage. In this case, oil flowing from the oil hole 40 flows through an oil hole 45 formed in the pivot shaft (inclined rotation shaft) 5 of the trunnion 6 into the back surface side of the trunnion 6. By the way, in FIG. 7, reference character 42 designates a plug which is press-fitted into the oil hole 45.
However, in the above lubricating oil passage forming method, there arises a problem. That is, the trunnion 6 has hardness exceeding HRC30 as a whole in order to secure the strength thereof, while this hardness is also required of the trunnion shaft 29 which is formed integrally with the trunnion 6. That is, in the above lubricating oil passage forming method, it is necessary to drill a small-diameter hole in the trunnion shaft 29 having the hardness of HRC30 or higher, which results in the lowered working precision. Therefore, even when the number of steps for working the trunnion 6 and trunnion shaft 29 can be reduced by working them as an integral body, the complicated drilling operation makes it impossible to reduce the manufacturing cost thereof sufficiently.